Mastitis in dairy herds is one of the most costly and difficult diseases encountered by dairy producers. Conventional therapies aimed at curing clinical mastitis include intra-mammary antimicrobial therapy. Despite the commercial availability of numerous intra-mammary antimicrobial products, cure rates for clinical mastitis remain perplexingly low: 46% for Streptococcus spp., 21% for Staphylococcus spp., and only 9% for Staphylococcus aureus mastitis. See Wilson et al. (1996) National Mastitis Council Proceedings 164-165, and Crandall et al. (2005) NMC Annual Meeting Proceedings 215-216. Thus, dairy producers often manage the disease simply by culling mastitis-prone animals from their herds.
Because of the difficulty in treating mastitis, prevention of new intra-mammary infections is a major focus in the dairy industry. The rate of new infections is significantly higher during the dry period as compared to new infections during the lactating period. (For example, one study showed that 61% of all new gram-negative intra-mammary infections occurred during the dry period. See Todhunter et al. (1995) J. Dairy Sci. 78:2366.) The three-week period immediately following dry off, and the two weeks prior to calving, are periods particularly prone to new infections. Thus, in recent years dairy producers have focused a considerable amount of effort in “preventive maintenance” of cows during their dry period.
In April of 2003, an internal (or “intra-mammary”) teat sealant (ITS) for use in dry cows was introduced in the US market. Marketed in the US under the “ORBESEAL” trademark (U.S. Pat. Nos. 2,772,198 and 3,120,693), the product was developed in New Zealand. The “ORBESEAL”-brand ITS introduced into the US market contains 65% w/w bismuth sub-nitrate dispersed in a viscous paste. The ITS product does not contain any antibiotics, nor does the product contain any active antimicrobial agents. The ITS is injected into the teat end using a tubular applicator syringe, in the same fashion as applying a dry cow antibiotic. The ITS product fills the fissures and folds of the teat canal, thereby creating a physical barrier to pathogens. See U.S. Pat. No. 6,254,881, issued Jul. 3, 2001, incorporated herein by reference.
Initial studies of the “ORBESEAL”-brand product in New Zealand concluded that the product functioned as well as a broad spectrum, long-acting intra-mammary antibiotic in preventing new intra-mammary infections at calving and in preventing clinical appearance of mastitis through the first five (5) months of lactation. See Woolford et al. (1998) New Zealand Veterinary Journal 46:1. A more recent study in the US also concluded that this ITS product improved the udder health of cows already infused with cloxacillin benzathine. See Godden et al. (2003) J. Dairy Sci. 86:3899-3911. Thus, the “ORBESEAL”-brand ITS has proven to be an effective tool in reducing the number of new cases of mastitis in dairy cows during their dry period. Despite its relatively recent introduction into the US market, the “ORBESEAL”-brand product has enjoyed widespread market acceptance and is used extensively in US dairy herds. In short, the “ORBESEAL”-branded product is very good for its intended purpose of preventing mastitis.
Subsequent to the introduction of the “ORBESEAL”-brand ITS product in the US, a visual defect in aged dairy products, most notably aged cheddar cheeses, began to appear. The visual defect takes the form of small, black spots (roughly 0.5 to 5 mm in diameter) that appear throughout the aged cheese. The spots are a purely aesthetic, visual defect that lowers the graded quality (and hence the market value) of the cheese affected with the problem. The spots are not accompanied by any organoleptic defect in the cheese. Cheese affected with the black spots is saleable, albeit at a lower grade than unaffected cheeses. The defect has been termed “black spot defect” (BSD).